Semiconductor wafers are used in manufacturing integrated circuits (ICs). ICs commonly incorporate a large number of microelectronic metal oxide semiconductor (MOS) devices, such as MOS capacitors and MOS field effect transistors (MOSFETs). In a MOS device, a dielectric material is placed on top of a semiconductor substrate, and metal is placed on the top of the dielectric material to form a metal gate. When a voltage is applied across the device, a conducting channel is induced in the semiconductor substrate via the field effect. This channel can contain electrons (e.g., in an nMOS device), or holes (e.g., in a pMOS device), opposite in type to the substrate. In some cases, a complementary MOS device (CMOS) can be constructed using nMOS and pMOS devices in combination.
Metrology is used to monitor various parameters associated with devices forming integrated circuits and maintain quality of the ICs. Non-contact techniques may be used to monitor some of these parameters.